Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Studies of pear-shaped nuclei using accelerated radioactive beams

Abstract

There is strong circumstantial evidence that certain heavy, unstable atomic nuclei are ‘octupole deformed’, that is, distorted into a pear shape. This contrasts with the more prevalent rugby-ball shape of nuclei with reflection-symmetric, quadrupole deformations. The elusive octupole deformed nuclei are of importance for nuclear structure theory, and also in searches for physics beyond the standard model; any measurable electric-dipole moment (a signature of the latter) is expected to be amplified in such nuclei. Here we determine electric octupole transition strengths (a direct measure of octupole correlations) for short-lived isotopes of radon and radium. Coulomb excitation experiments were performed using accelerated beams of heavy, radioactive ions. Our data on 220Rn and 224Ra show clear evidence for stronger octupole deformation in the latter. The results enable discrimination between differing theoretical approaches to octupole correlations, and help to constrain suitable candidates for experimental studies of atomic electric-dipole moments that might reveal extensions to the standard model.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.

$32.00

All prices are NET prices.

Figure 1: Representative γ-ray spectra following the bombardment of 2 mg cm−2 60Ni and 120Sn targets by 220Rn and 224Ra.
Figure 2: Partial level-schemes for 220Rn and 224Ra, showing the excited states of interest for this work.
Figure 3: The values of the E2 and E3 intrinsic moments, Qλ (I, I′).
Figure 4: Graphical representation of the shapes of 220Rn and 224Ra.
Figure 5: Values of Qλ for low-lying transitions in nuclei as a function of N.

References

  1. Pospelov, M. & Ritz, A. Electric dipole moments as probes of new physics. Ann. Phys. 318, 119–169 (2005)

    ADS  CAS  Article  Google Scholar 

  2. Griffith, W. C. et al. Improved limit on the permanent electric dipole moment of 199Hg. Phys. Rev. Lett. 102, 101601 (2009)

    ADS  CAS  Article  Google Scholar 

  3. Spevak, V., Auerbach, N. & Flambaum, V. V. Enhanced T-odd, P-odd electromagnetic moments in reflection asymmetric nuclei. Phys. Rev. C 56, 1357–1369 (1997)

    ADS  CAS  Article  Google Scholar 

  4. Dobaczewski, J. & Engel, J. Nuclear time-reversal violation and the Schiff moment of 225Ra. Phys. Rev. Lett. 94, 232502 (2005)

    ADS  CAS  Article  Google Scholar 

  5. Ellis, J., Lee, J. & Pilaftsis, A. Maximal electric dipole moments of nuclei with enhanced Schiff moments. J. High Energy Phys. 2011, 045 (2011)

    Article  Google Scholar 

  6. Guest, J. R. et al. Laser trapping of 225Ra and 226Ra with repumping by room-temperature blackbody radiation. Phys. Rev. Lett. 98, 093001 (2007)

    ADS  CAS  Article  Google Scholar 

  7. Cocks, J. et al. Spectroscopy of Rn, Ra and Th isotopes using multi-nucleon transfer reactions. Nucl. Phys. A 645, 61–91 (1999)

    ADS  Article  Google Scholar 

  8. Dahlinger, M. et al. Alternating parity bands and octupole effects in 221Th and 223Th. Nucl. Phys. A 484, 337–375 (1988)

    ADS  Article  Google Scholar 

  9. Butler, P. A. & Nazarewicz, W. Intrinsic dipole moments in reflection-asymmetric nuclei. Nucl. Phys. A 533, 249–268 (1991)

    ADS  Article  Google Scholar 

  10. Nazarewicz, W. et al. Analysis of octupole instability in medium-mass and heavy nuclei. Nucl. Phys. A 429, 269–295 (1984)

    ADS  Article  Google Scholar 

  11. Möller, P. et al. Axial and reflection asymmetry of the nuclear ground state. At. Data Nucl. Data Tables 94, 758–780 (2008)

    ADS  Article  Google Scholar 

  12. Bonche, P., Heenen, P. H., Flocard, H. & Vautherin, D. Self-consistent calculation of the quadrupole-octupole deformation energy surface of 222Ra. Phys. Lett. B 175, 387–391 (1986)

    ADS  CAS  Article  Google Scholar 

  13. Egido, J. & Robledo, L. Microscopic study of the octupole degree of freedom in the radium and thorium isotopes with Gogny forces. Nucl. Phys. A 494, 85–101 (1989)

    ADS  Article  Google Scholar 

  14. Rutz, K., Maruhn, J. A., Reinhard, P.-G. & Greiner, W. Fission barriers and asymmetric ground states in the relativistic mean-field theory. Nucl. Phys. A 590, 680–702 (1995)

    ADS  Article  Google Scholar 

  15. Engel, J., Bender, M., Dobaczewski, J., Jesus, J. H., d & Olbratowski, P. Time-reversal violating Schiff moment of 225Ra. Phys. Rev. C 68, 025501 (2003)

    ADS  Article  Google Scholar 

  16. Robledo, L. M. & Bertsch, G. F. Global systematics of octupole excitations in even-even nuclei. Phys. Rev. C 84, 054302 (2011)

    ADS  Article  Google Scholar 

  17. Shneidman, T. M., Adamian, G. G., Antonenko, N. V., Jolos, R. V. & Scheid, W. Cluster interpretation of properties of alternating parity bands in heavy nuclei. Phys. Rev. C 67, 014313 (2003)

    ADS  Article  Google Scholar 

  18. Buck, B., Merchant, A. C. & Perez, S. M. Negative parity bands in even–even isotopes of Ra, Th, U and Pu. J. Phys. G 35, 085101 (2008)

    ADS  Article  Google Scholar 

  19. Zamfir, N. V. & Kusnezov, D. Octupole correlations in the transitional actinides and the spdf interacting boson model. Phys. Rev. C 63, 054306 (2001)

    ADS  Article  Google Scholar 

  20. Frauendorf, S. Heart-shaped nuclei: condensation of rotational-aligned octupole phonons. Phys. Rev. C 77, 021304 (2008)

    ADS  Article  Google Scholar 

  21. Butler, P. A. & Nazarewicz, W. Intrinsic reflection asymmetry in atomic nuclei. Rev. Mod. Phys. 68, 349–421 (1996)

    ADS  CAS  Article  Google Scholar 

  22. Robledo, L. M. & Bertsch, G. F. Electromagnetic transition strengths in soft deformed nuclei. Phys. Rev. C 86, 054306 (2012)

    ADS  Article  Google Scholar 

  23. Wollersheim, H. J. et al. Coulomb excitation of 226Ra. Nucl. Phys. A 556, 261–280 (1993)

    ADS  Article  Google Scholar 

  24. Voulot, D. et al. Radioactive beams at REX–ISOLDE: present status and latest developments. Nucl. Instrum. Methods B 266, 4103–4107 (2008)

    ADS  CAS  Article  Google Scholar 

  25. Eberth, J. et al. MINIBALL A Ge detector array for radioactive ion beam facilities. Prog. Part. Nucl. Phys. 46, 389–398 (2001)

    ADS  CAS  Article  Google Scholar 

  26. Ostrowski, A. et al. CD: A double sided silicon strip detector for radioactive nuclear beam experiments. Nucl. Instrum. Methods A 480, 448–455 (2002)

    ADS  CAS  Article  Google Scholar 

  27. Bell, R. E., Bjornholm, S. & Severiens, J. C. Half lives of first excited states of even nuclei of Fm, Ra, Th, U, and Pu. Kgl. Danske Vid. Selsk. Mat.-Fys. Medd. 32, 1–48 (1960)

    Google Scholar 

  28. Neal, W. R. & Kraner, H. W. Mean lives of excited rotational states of heavy even-even nuclei. Phys. Rev. 137, B1164–B1174 (1965)

    ADS  Article  Google Scholar 

  29. Liang, C. F., Paris, P., Ruchowska, E. & Briancon, C. A new isotope 85 220At135 . J. Phys. G 15, L31–L33 (1989)

    ADS  CAS  Article  Google Scholar 

  30. Artna-Cohen, A. Nuclear data sheets for A = 224. Nucl. Data Sheets 80, 227–262 (1997)

    ADS  CAS  Article  Google Scholar 

  31. Cline, D. Quadrupole and octupole shapes in nuclei. Nucl. Phys. A 557, 615–634 (1993)

    ADS  Article  Google Scholar 

  32. Nazarewicz, W. & Tabor, S. L. Octupole shapes and shape changes at high spins in the Z 58, N 88 nuclei. Phys. Rev. C 45, 2226–2237 (1992)

    ADS  CAS  Article  Google Scholar 

  33. Ibbotson, R. W. et al. Quadrupole and octupole collectivity in 148Nd. Nucl. Phys. A 619, 213–240 (1997)

    ADS  Article  Google Scholar 

  34. Leander, G. A. & Chen, Y. S. Reflection-asymmetric rotor model of odd A 219–229 nuclei. Phys. Rev. C 37, 2744–2778 (1988)

    ADS  CAS  Article  Google Scholar 

  35. Riley, L. A. et al. Conversion electron-γ coincidences and intrinsic reflection asymmetry in 219Ra. Phys. Rev. C 62, 021301 (2000)

    ADS  Article  Google Scholar 

  36. Ackermann, B. et al. Level structure of 217Rn and 221Ra investigated in the alpha-decay 225Th → 221Ra → 217Rn. Z. Phys. A 332, 375–381 (1989)

    ADS  CAS  Google Scholar 

  37. Nosek, D., Sheline, R. K., Sood, P. C. & Kvasil, J. Microscopic structures of parity doublets in the 151Pm, 153Eu and 155Eu nuclei. Z. Phys. A 344, 277–283 (1993)

    ADS  CAS  Article  Google Scholar 

  38. Rząca-Urban, T. et al. Reflection symmetry of the near-yrast excitations in 145Ba. Phys. Rev. C 86, 044324 (2012)

    ADS  Article  Google Scholar 

  39. Poynter, R. J. et al. Observation of unexpectedly small E1 moments in 224Ra. Phys. Lett. B 232, 447–451 (1989)

    ADS  CAS  Article  Google Scholar 

  40. Goriely, S., Hilaire, S., Girod, M. & Péru, S. First Gogny-Hartree-Fock-Bogoliubov nuclear mass model. Phys. Rev. Lett. 102, 242501 (2009)

    ADS  CAS  Article  Google Scholar 

  41. Greenlees, P. T. et al. First observation of excited states in 226U. J. Phys. G 24, L63–L70 (1998)

    CAS  Google Scholar 

  42. Penescu, L., Catherall, R., Lettry, J. & Stora, T. Development of high efficiency versatile arc discharge ion source at CERN ISOLDE. Rev. Sci. Instrum. 81, 02A906 (2010)

    CAS  Article  Google Scholar 

  43. Wolf, B. H. et al. First radioactive ions charge bred in REXEBIS at the REX-ISOLDE accelerator. Nucl. Instrum. Methods Phys. Res. B 204, 428–432 (2003)

    ADS  CAS  Article  Google Scholar 

  44. Martin, M. J. Nuclear data sheets for A = 208. Nucl. Data Sheets 108, 1583–1806 (2007)

    ADS  CAS  Article  Google Scholar 

  45. Bemis, C. E. et al. E2 and E4 transition moments and equilibrium deformations in the actinide nuclei. Phys. Rev. C 8, 1466–1480 (1973)

    ADS  CAS  Article  Google Scholar 

  46. Baktash, C. & Saladin, J. X. Determination of E2 and E4 transition moments in 232Th. Phys. Rev. C 10, 1136–1139 (1974)

    ADS  CAS  Article  Google Scholar 

  47. McGowan, F. K. et al. Coulomb excitation of vibrational-like states in the even-A actinide nuclei. Phys. Rev. C 10, 1146–1155 (1974)

    ADS  CAS  Article  Google Scholar 

  48. McGowan, F. & Milner, W. Coulomb excitation of states in 232Th. Nucl. Phys. A 562, 241–259 (1993)

    ADS  CAS  Article  Google Scholar 

  49. Singh, S., Jain, A. & Tuli, J. K. Nuclear data sheets for A = 222. Nucl. Data Sheets 112, 2851–2886 (2011)

    ADS  CAS  Article  Google Scholar 

  50. Artna-Cohen, A. Nuclear data sheets for A = 228. Nucl. Data Sheets 80, 723–786 (1997)

    ADS  Article  Google Scholar 

Download references

Acknowledgements

The support of the ISOLDE Collaboration and technical teams is acknowledged. This work was supported by the following Research Councils: STFC (UK), BMBF(Germany; 05P12RDCIA, 06DA9036I, 06KY9136I and 06KY205I), HIC for FAIR (Germany), FWO-Vlaanderen (Belgium), Belgian Science Policy Office (IAP-BriX network P7/12), Academy of Finland (contract no. 131665), DOE (US; DE-AC52-07NA27344 and DE-FG02-04ER41331), NSF (US), MICINN (Spain; FPA2009-08958 and FIS2009-07277), Consolider-Ingenio 2010 Programmes (Spain; CPAN CSD2007-00042 and MULTIDARK CSD2009-00064), Polish Ministry for Science and Higher Education (grant no. 589/N-G-POOL/2009/0), EC via I3-EURONS (FP6 contract no. RII3-CT-2004-506065), MC Fellowship scheme (FP7 contract PIEF-GA-2008-219175) and IA-ENSAR (FP7 contract 262010).

Author information

Authors and Affiliations

Authors

Contributions

Instrument set-up: M.A., C.B., A.B., T.D., H.D.W., L.P.G., J.K., J.P., P.R., M. Seidlitz, B.S., M.J.V. and N.W. DAQ and on-line analysis: A.B., L.P.G., R.L. and N.W. Data analysis and interpretation: L.P.G., P.A.B., D.C., A.B.H., M. Scheck and M.Z. REX development and set-up: F.W., D.V. and J.C. Primary target: T.S. Preparation of manuscript: P.A.B., L.P.G., T.C., A.B., D.G.J., Th.K., J.P., P.R., M. Scheck, P.V.D. and N.W. Theoretical interpretation: L.M.R. All authors except L.M.R. took part in the experiments.

Corresponding author

Correspondence to P. A. Butler.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Gaffney, L., Butler, P., Scheck, M. et al. Studies of pear-shaped nuclei using accelerated radioactive beams. Nature 497, 199–204 (2013). https://doi.org/10.1038/nature12073

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature12073

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing